1. Field
One embodiment of the invention relates to a method of recording or reproducing an encryption key or the like, information requested to have a high confidentiality. This invention further relates to a reproducing apparatus which uses stored or recorded highly confidential data.
2. Description of the Related Art
In recent years, various reproducing apparatuses capable of reproducing AV contents recorded on a disc medium, such as a DVD (Digital Versatile Disc), have been developed. Such reproducing apparatuses include a recorder with a dedicated player or a reproducing function, and a personal computer provided with a DVD disc drive and a reproducing software program. Stream data recorded on a DVD disc or the like to be played back on such a reproducing apparatus has been encrypted to prevent the data from being copied. An encryption scheme conforming mostly to the CCS (Content Scramble System) method has been applied to the encrypted stream data part. As a higher encryption scheme, AACS (Advanced Access Content System) has been proposed (refer to Jpn. Pat. Appln. KOKAI Publication No. 2005-39480). When the AACS method is used, for example, a reproducing apparatus set manufacturer gets a specific key set from a key tree the licenser has, encrypts different combinations of keys, and incorporates the encrypted keys into individual reproducing apparatuses.
In the AACS, to prevent unauthorized copying, data called MKB (Media Key Block) is used. MKB is mathematically systematic data obtained by encrypting a media key (Km), a base key of content encryption, using an aggregate of device keys (Kd) provided as private keys in reproducing apparatuses. Moreover, in MKB, information on unauthorized apparatuses has been recorded, thereby preventing the unauthorized apparatuses from taking out the media key (Km).
Since information on unauthorized apparatuses is updated, a new MKB has to be used. Therefore, in the AACS, there are three types of MKB: Lead-in MKB embedded in the Lead-in Area of a medium, Read Write MKB stored as a file in a medium, and Device MKB stored in its internal nonvolatile memory by the apparatus itself. Of them, the latest MKB is supposed to be written over Read Write MKB.
Content protection using such MKB is a technology for effectively preventing unauthorized use of DVD media contents. To maintain this functionality, MKB has to be updated as needed. Since the update is made by writing MKB over Read Write MKB, frequent updating of MKB leads to a decrease in the response of the system.